Primary Structure of Human Fibrinogen and Fibrin

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Abstract
The cyanogen bromide fragment, N-DSK, containing the NH2-terminal portions of the three chains of fibrinogen, was found to exist in dimeric and polymeric forms. These different forms gave rise to identical chain fragments on reduction and alkylation. The Bβ chain of N-DSK from fibrinogen and the β chain of N-DSK from fibrin were isolated and characterized. The Bβ chain fragment has a blocked NH2-terminal residue, and fibrinopeptide B is released on digestion with thrombin. The 1 chain fragment has glycine as NH2-terminal residue. The molecular weight of the Bβ chain fragment is 12200 as determined by ultracentrifugal analysis. Gel electrophoresis in sodium dodecyl sulphate gave the molecular weights of 14000 and 13000 for the Bβ chain and β chain fragments, respectively. The NH2-terminal Bβ chain fragment consists of 118 amino acid residues and the β chain fragment of 104 residues. The amino acid sequence of β chain fragment is identical to Bβ chain fragment except for the fibrinopeptide B portion. The isolation of a Bβ-related fragment (Bβ+), with a molecular weight of 30000, is also reported. The presence of Bβ+ was explained on the basis of incomplete cleavage at the Met-118 residue during treatment with cyanogen bromide. Some functional aspects of the Bβ chain fragment are discussed.